The present invention relates to a liquid crystal display (LCD) device, and more particularly to an apparatus and method for automatic brightness control for use in the LCD device.
An LCD or thin film transistor liquid crystal display (TFT-LCD) module is generally used as a display device in a system such as a portable computer, a television set, and a monitor. FIG. 1 shows a structure of a general LCD module 100. Referring now to FIG. 1, the LCD module 100 comprises an LCD panel 10 for displaying all sorts of information having a liquid crystal material between two glass substrates, a driving unit having driving circuits 20, 30 for driving the LCD panel 10 and a timing controller 40 for generating control signals to control the driving circuits 20, 30, a backlight 60 for guiding light to the LCD panel 10, and a chassis (not shown) for holding and protecting the LCD panel 10 and components of the backlight 60.
The backlight 60 includes an inverter 62, a fluorescent lamp 64 such as a cold cathode fluorescent tube (CCFT) or a hot cathode fluorescent tube (HCFT), and a plurality of sheets including a reflecting sheet 66 for guiding light to the front. The backlight 60 functions to guide light from the fluorescent lamp 64 to the LCD panel 10. The LCD panel 10 displays color images by shielding or passing light from the backlight 60 through each pixel therein in response to a signal voltage of respective corresponding pixel inputted from the driving circuits 20, 30.
FIG. 2 is a block diagram showing a conventional backlight brightness control scheme of the LCD module 100 when it is used as a display device in a portable computer or a desktop computer. The portable computer or desktop computer is generally driven by the direct current, whereas the backlight 60 is lit up on by the alternating current. Thus, it is essential for the LCD module 100 to have the inverter 62 for transforming the direct current into the alternating current as shown in the drawing. The inverter 62 includes a dimming circuit (not shown) to control the brightness of the fluorescent lamp 64 as well as to transform the direct current into the alternating current, as well known in the art.
Referring to FIG. 2, in the operation, as a brightness control command is inputted by the computer operation of user, a central processing unit (CPU) or main body 200 of the computer generates a brightness control voltage CTL_V for controlling brightness, to the inverter 62. In response to the brightness control voltage CTLxe2x80x94V from the main body 200, the dimming circuit of the inverter 62 controls an amount of current of the fluorescent lamp 64 to adjust the brightness of the backlight 60. For example, If the computer is a portable computer, the brightness control voltage CTL_V is within the range of 0 through 3.3 V. That is, when the brightness control voltage CTL_V is 0 V, a most dark brightness, i.e., black appears, and when the brightness control voltage CTL_V is 3.3 V, a most light brightness, i.e., white appears.
However, the conventional brightness control scheme of the LCD module is characterized that once the brightness is controlled, a value or level of the controlled brightness is unchanged even though the properties of data for each picture or frame to be displayed through the LCD module 100 vary. That is, the conventional brightness control scheme may raise a problem that increases the power consumption since the brightness is uniformly maintained regardless of a change in light and darkness between frames or a quick change of pictures or frames such as in motion images. Also, a picture of red (R) or blue (B) color of low transmissivity is not greatly brightened, no matter how much the brightness of the backlight may be increased. Therefore, in this case, the effect obtained through increasing the brightness is small compared to the power consumption increase.
Therefore, it is an object of the present invention to provide an improved apparatus and method for automatic brightness control for use in an LCD device, which can automatically control a brightness for each picture by controlling a duty rate for each picture automatically.
It is another object of the present invention to provide an improved apparatus and a method for automatic brightness control in an LCD device that can properly accommodate a brightness control by a user request and an automatic brightness control for each picture without conflicts therebetween.
It is other object of the present invention to provide an improved apparatus and a method for automatic brightness control for use in an LCD device which can improve a contrast for each picture displayed through an LCD module.
It is further object of the present invention to provide an improved apparatus and a method for automatic brightness control for use in an LCD device, which can reduce the power consumption of an LCD module, by controlling a brightness according to data characteristic for each picture.
It is still other object of the present invention to provide an improved apparatus and a method for automatic brightness control for use in an LCD device, which can control a brightness of backlight corresponding to a state of red (R), green (G) and blue (B) colors of a picture to be displayed in the LCD device, and thereby reduce the power consumption of the LCD module.
These and other objects are provided, according to one aspect of the present invention, by an apparatus for automatic brightness control for use in an LCD device having a backlight, comprising control signal generating means for receiving an image data to be displayed through the LCD device, calculating an average gray level of the image data, and generating a brightness control signal in proportion to the average gray level, and an inverter for controlling a brightness of the backlight automatically in response to the brightness control signal from the control signal generating means.
According to another aspect of the present invention, there is provided an apparatus for automatic brightness control for use in an LCD device having a backlight comprising, first control signal generating means for receiving an image data to be displayed through the LCD device, calculating an average gray level of the image data, and generating a first brightness control signal in proportion to the average gray level, second control signal generating means for generating a second brightness control signal to control a brightness of the backlight, by means of the operation of user, third control signal generating means for generating a third brightness control signal in response to the first and second brightness control signals from the first and second control signal generating means, and an inverter for controlling the brightness of the backlight in response to the third brightness control signal from the third control signal generating means.
According to other aspect of the present invention, there is provided a method for automatic brightness control for use in an LCD device comprising the steps of, calculating an average gray level of an image data to be displayed through the LCD device, generating a first brightness control signal in proportion to the average gray level, generating a second brightness control signal through the main body of the computer and controlling a brightness of backlight in response to a third brightness control signal generated according to the first and second brightness control signals.
According to still other aspect of the present invention, there is provided an apparatus for automatic brightness control for use in an LCD device having a backlight, which is used with a host of outputting a video information, comprising control signal generating means for receiving a pixel data corresponding to the video information, determining a color state of the pixel data, and generating a brightness control signal having a duty rate for controlling a brightness of the backlight corresponding to the determined color state, and an inverter for controlling automatically the brightness of the backlight in response to the brightness control signal from the control signal generating means.
In a preferred embodiment, the brightness control signal has a duty rate reduced in order of green, red, and blue when the determined color state is green, red, and blue. The duty rate of the brightness control signal is set to have a rate of green: red:blue=1:0.66:0.49 when the determined color state is green, red, and blue. The control signal generating means can be formed of a timing controller.
In the preferred embodiment, the control signal generating means includes a control unit for controlling various operations of the control signal generating means to determine the color state of the pixel data and to generate the brightness control signal, a pixel data acquisition and conversion unit for receiving the pixel data from the host and converting the pixel data according to the determined color state under the control of the control unit, a computing unit for computing the converted data logically and outputting a certain data under the control of the control unit, a down-counter for down-counting the certain data under the control of the control unit, and a pulse generator for generating the brightness control signal corresponding to an output signal of the down-counter. The control unit controls to generate the brightness control signal corresponding to an output signal of the down-counter until it comes to a logic low level.
According to other aspect of the present invention, there is provided a method for automatic brightness control for use in an LCD device having a backlight, which is used with a host of outputting a video information, comprising the steps of receiving a pixel data corresponding to the video information, determining a color state of the pixel data, converting the pixel data according to the determined color state, determining whether the pixel data is a last data of one horizontal line period, outputting a brightness control signal corresponding to the pixel data when the pixel data is the last data of one horizontal line period, and controlling a brightness of the backlight in response to the brightness control signal.
In a preferred embodiment, the converting step comprises converting the pixel data to have a duty rate corresponding to a brightness reduced in order of green, red, and blue when the determined color state is green, red, and blue. Preferably, the pixel data are converted into data corresponding to 100%, 66% and 49% of a maximum brightness when the determined color state is green, red, and blue, respectively.